U.S. Pat. No. 4,384,797 to Anderson et al, filed Aug. 13, 1981, entitled "Single Laminated Element for Thermal Printing and Lift-Off Correction, Control Therefor and Process," and assigned to the same assignee to which this application is assigned describes and claims lift-off correction using a thermal printer employing intermediate heat for correction. That application discloses a transfer medium which prints in the normal manner having a resistive layer of polycarbonate, an intermediate lamination of aluminum, and a transfer layer formulated to print at normal printing temperatures and to correct at temperatures less than the printing temperatures.
This invention employs the same transfer layer formulation as that application, while achieving printing and correction at substantially lower temperatures. This is achieved by employing a layer which facilitates release between the aluminum and the transfer layer.
U.S. Pat. No. 4,320,170 to Hugh T. Findlay, filed Dec. 8, 1980, entitled "Polyurethane Ribbon For Non-Impact Printing" and assigned to the same assignee to which this application is assigned describes and claims a thermal ribbon having a resistive layer of polyurethane. The best-made embodiment of this invention employs essentially the same resistive layer except that the urethane is blended as a copolymer with ethyl acrylate to provide greater thermal stability.
The essential element of this invention which permits printing and lift-off correction at lower temperatures is the release layer. Such a release layer is disclosed in an article entitled "Release-Adhesive Interlayers For Lift-Off Correction" in IBM Technical Disclosure Bulletin, Vol. 24, No. 5 (October 1981), page 2247 by C. W. Anderson et al. That article discloses ethylene acrylic acid copolymer as one interlayer material, which material is believed to be essentially identical with the material of the preferred embodiment of this invention. The basic difference between that article and the invention here described and claimed is in the characteristics of the ink layer. That ink layer was a polyamide (misspelled polyamid in the publication), carbon black, and a plasticizer blended to be of high viscosity under heat. That ink material does not function at intermediate heat to become tacky for lift-off correction of characters printed from the ink. Lift-off correction of the polyamide ink is by a separate adhesive element, such as by a conventionally used adhesive tape. The subject invention improves a prior art ribbon which both prints at normal temperature and corrects at a lower temperature.
An interlayer in a thermal printing system employing an adhesive top layer is disclosed in an article entitled "Delayed Tack Ribbon for Laser Transfer and Other Printing," in IBM Technical Disclosure Bulletin, Vol. 19, No. 2 (July 1976) page 672 by C. A. Bruce and C. E. Stratton. Release layers in conventional transfer mediums are shown in U.S. Pat. Nos. 3,337,361 to La Count and 3,170,809 to Barbour. Polymers as the resistive layer in a thermal ribbon having urethane and non-urethane major parts are shown in the prior art in U.S. Pat. No. 4,269,892 to Shattuck et al.